1、Mthode pour la dtection de dfauts dans les particules magntiques Methode fr die Magnetpulver-Riprfung British Standards Institution ES1 BS*b072 AL Lb24bb9 0065002 L M BS 6072 : 1981 I Contents Page Foreword Inside front cover Cooperating organizations Back cover Method O. Introduction 1. Scope 2. Re
2、ferences 3. Definitions 4. Magnetizing apparatus and associated equipment 5. Detecting media 6. Safety precautions 7. Testing procedures 8. Surface preparation 9. Magnetization 1 O. Current flow technique 1 1. Threading bar or cable technique 12. Rigid coil technique 13. Flexible cable technique (co
3、il technique 14. Flexible cable technique (using a flexible 1 5. Magnetic flow technique 16. Induced current flow technique 17. Current flow (prods) technique 18, Application of detecting medium 19. Viewing 20. Recording of indications 2 I. Reporting 22. Demagnetization 23. Cleaning using a flexible
4、 cable) cable adjacent to the test surface) 7 7 7 8 8 9 9 9 10 10 11 Appendices A. Selection of test techniques for magnetizing material or components of specific geometric shape 15 B. Methods for determining the inspected areas when using the current flow (prods) technique 19 19 21 E. Preservation
5、of indications 23 C. Test pieces and test procedure D. Report, technique and procedure sheets Foreword Over the past years, several British Standards have been issued describing the application of magnetic particle flaw detection techniques to specific products. It was accordingly considered that it
6、 would now be opportune to prepare a comprehensive basic standard for this particular method of non-destructive testing. This British Standard has accordingly been prepared under the direction of the Mechanical Engineering Standards Committee and due account has been taken of the corresponding aeros
7、pace standard, BS M 35 : 1970 Method for magnetic particle flaw detection of materials and components, which provide the basis for this work. This British Standard has been prepared to provide detailed information on magnetic particle flaw detection to which other BSI committees responsible for the
8、application of appropriate techniques to specific products and establishing acceptance criteria can make reference. It is, however, recognized that some variation in basic techniques may be required for particular applications. For example, in the derivation of the formulae covering the flexible cab
9、le technique described in clause 13, certain assumptions are involved and, in some circumstances, Page Tables 1, Factor by which indicated current values 2. Current values for general engineering 3. Current values for aerospace applications 4. List of testing techniques 5. Test techniques for materi
10、al or components 6. Dimensions of standard test piece for current are multiplied to obtain peak values 4 applications 6 6 15 of specific geometric shape 18 flow checking 20 Fig u res 1. Current flow technique 11 2. Threading bar or cable technique 3. Flexible threading bar technique through the spec
11、imen) 11 5. Coil technique 11 round the specimen) 12. 7. Magnetic flow technique 12 11 11 4. Flexible cable technique (using cable wound 6. Flexible cable technique (using cable wound 8. Induced current flow technique 9. Current flow technique (prods) 13 13 1 O. Search pattern which is acceptable wh
12、en using the current flow (prods) technique to inspect flat surfaces and those with radii of curvature greater than half the prod spacing (peak current value not less than 7500 amps per metre of prod spacing) (prods) technique when the peak current value is 4700 amps per metre of prod spacing 14 12.
13、 Details of standard test piece for current 13. Test piece for checking magnetic flow and 14 1 1. Search pattern for the curent flow flow checking 20 coil magnetization 21 there may be practical limitations in the application of this technique. Consideration is therefore being given to the preparati
14、on of a further BSI publication (a Published Document (PD) in which the background considerations which have been taken into account in the preparation of this standard will be explained. It is emphasized that the effectiveness of magnetic particle inspection rests on the technical competence of the
15、 personnel employed on such work and their ability to interpret the indications given by the techniques. In interpreting results from magnetic particle inspection, it is necessary to distinguish between relevant indications from flaws and non-relevant indications arising from other causes. Magnetic
16、particle flaw detection is often used in conjunction with other testing methods. The use of any non-destructive testing methods should always be considered in relation to testing and inspection as a whole. When such methods are specified, the most suitable and economic method of inspection compatibl
17、e with the ultimate application for the product should always be employed. BS 6072 : 1981 British Standard Method for Magnetic particle flaw detection O. Introduction 0.1 Basic principles. Magnetic particle flaw detection depends basically on sensing the discontinuous change between the permeability
18、 of the ferromagnetic material and the permeability of the flaw. When the test piece is suitably magnetized, favourably orientated flaws, at or near the magnetized surface, distort the magnetic field, causing local flux-leakage fields. If finely divided, ferromagnetic particles are applied to the su
19、rface of the magnetized test piece, they are attracted by the flux-leakage field and accumulate at the site of the flaw, thus enabling it to be detected. 0.2 Optimum flaw direction. Maximum sensitivity is achieved when the flaw lies at rightangles to the magnetic flux, but the sensitivity is not red
20、uced below the effective level if the flaw is orientated at an angle of up to 45“ from the optimum direction. Beyond 45“, the sensitivity is diminished appreciably. For this reason, the complete examination of any surface requires the flux to be passed in fwo directions a right angles to each other,
21、 in separate operations. 0.3 Advantages 0.3.1 Magnetic particle flaw detection can detect cracks, non-metallic inclusions and other discontinuities in or near the surface of ferromagnetic materials. 0.3.2 The sensitivity of the inspection is not greatly impaired by the presence of foreign matter wit
22、hin the flaws, unless the contaminant has magnetic properties similar to those of the test piece. 0.3.3 It is possible to inspect components that have been treated with a non-magnetic coating (eqg. cadmium plate or paint) not greater than 50 pm thick, with only slight loss of sensitivity. 0.4 Limita
23、tions 0.4.1 The method cannot be used on non-magnetic materials. 0.4.2 Post-cleaning may be necessary in circumstances where the characteristics of the magnetic particles may be deleterious to the subsequent operation of the component. 0.4.3 The presence of surface coatings may reduce the sensitivit
24、y obtainable. 0.4.4 Flaws that do not break the surface give diffuse indications, and these indications become increasingly diffused with increase in the distance of the flaw below the surface. 0.4.5 Structural variations and certain types of segregation may give rise to misleading indications. 0.5
25、Personnel. Ail persons associated with magnetic particle flaw detection shall have been adequatey trained to the agreed levels appropriate to their responsibilities and be able to read the Jaeger J.2 chart* at a distance of 0.5 m. It is necessary for all operators and supervisors to observe the requ
26、irements of the Health and Safety at Work etc. Act 1974. 1. Scope This British Standard specifies techniques and procedures for magnetic particle flaw detection of ferromagnetic materials. Magnetic particle flaw detection is primarily used for the detection of surface-breaking flaws, particularly cr
27、acks. It can also detectflaws just below the surface, but its sensitivity diminishes rapidly with depth. 2. References The titles of the standards publications referred to in this standard are listed on the inside back cover. 3. Definitions For the purposes of this British Standard, the terms and de
28、finitions given in BS 3683 : Part 2 apply. 4. Magnetizing apparatus and associated equipment 4.1 Fixed installations 4.1-1 The installation shall be capable of enabling the component or material to be tested in accordance with the individual techniques specified. 4.1.2 The installation shall be equi
29、pped with controls for adjusting the excitation current, either continuously from zero to the maximum value, and/or in steps, such that any required current vaiues can be obtained within f 1 O % of the nominal. 4.1.3 The apparatus shall be equipped with an ammeter for measuring the current used in a
30、ny test. The ammeter shall have a scale length of 60 mm or greater, and shall comply with accuracy class 5 (f 5 %) of BS 89. The nominal waveform of the energizing current shall be shown on the apparatus, together with the manner in which the current is indicated by the meter of the apparatus, e.g.
31、peak, r.m.s., mean. 4.1.4 The installation shall have a reservoir tank to contain the magnetic flaw detection ink. Suitable means shall be provided for agitation of the ink prior to its application. If the tank is not fitted with a powered agitator, it shall be so designed that adequate agitation by
32、 a manually-operated paddle can be carried out frequently during the operation of the magnetizing equipment. *Obtainable from the American Society for Non-destructive Testing, 3200 Riverside Drive, Colombus, Ohio 4322 1 USA. 1 BSI BS*b072 131 BS 6072 : 1981 Air agitation of the ink shall not be used
33、 for kerosene or other mineral-oil based inks. 4.1.5 Means shall be provided for applying the detecting medium to the component under test, in such a manner that the flow complies with the requirements of clause 18. 4.1.6 The possible effect of magnetic constructional materials in a magnetic ink sup
34、ply system shall be carefully considered, since their magnetization may affect the functioning of the equipment. 4.2 Mobile and portable apparatus 4.2.1 The installation shall be capable of enabling the component or material to be tested in accordance with the individual techniques specified. Mobile
35、 and portable apparatus consisting of high current, low voltage supplies, shall be equipped with an ammeter for measuring the current used in any test. The ammeter shall have a scale length of 60 mm or greater, and shall comply with accuracy class 5 (_+ 5 %) of BS 89. The nominal waveform of the ene
36、rgizing current shall be shown on the apparatus, together with the manner in which the current is indicated by the meter of the apparatus, e.g. peak, rms., mean. 4.2.2 Where the technique requires provision for the adjustment of current, the equipment shall comply with the requirements for fixed ins
37、tallations. 4.2.3 Portable electromagnets (yokes) may be used without ammeters, provided the test requirements given in clause 15 are satisfied. 4.2.4 Auxiliary apparatus, such as contact prods, shall be provided in accordance with the techniques listed. 4.3 Control tests on equipment 4.3.1 General.
38、 The apparatus and ancillary equipment shall be checked at least every three months by a competent person to ensure its continuing efficacy. A record of the check shall be kept. 4.3.2 Ammeter. A check ammeter shall be used which shall apply to the same form factor and operate over approximately the
39、same range of current as the machine ammeter. It shall comply with accuracy class 5 (* 5 %) of BS 89 for industrial, portable instruments and have a scale length of 80 mm or greater. The difference between the machine ammeter and the check ammeter shall not exceed 1 O % of the scale reading of the m
40、achine ammeter at any reading within its effective range. 4.3.3 Functional test. A functional test shall be carried out by the operator before commencing work. The test shall be designed to ensure the proper functioning of both the equipment and the magnetic medium. Suitable test pieces and procedur
41、es are given in appendix C but, for certain types of fixed installation, the functional test described in appendix C is impracticable. Where this is the case, an alternative functional test shall be agreed between the interested parties. 5. Detecting media 5.1 Magnetic flaw detection inks and powder
42、s shall comply with the requirements of BS 4069. 5.2 If magnetic ink is reused or recirculated, a check on the total solids content shall be made immediately before use, or at intervals of two days during continuous use. Since magnetic ink will rapidly settle, thorough mixing of fluid and solid shal
43、l be maintained at all times. All checks lb246b 0065004 5 W shall be in accordance with BS 4069 and the solids content shall conform to the limits defined in that standard. 5.3 Magnetic ink shall be discarded and replaced when it becomes discoloured or contaminated by any foreign substance to the ex
44、tent that proper distribution and concentration of the suspension, or definition of the magnetic particle indication, is affected. 5.4 Magnetic inks shall not be mixed unless they are of the same type and specification and are supplied by the sa m e m a n uf a ctu re r. 5.5 The performance of fluore
45、scent magnetic ink used in a system where it is recirculated (.e. pumped) shall be assessed weekly by comparing its performance in revealing known flaws with the performance of a fresh sample of ink. 6. Safety precautions 6.1 General. It is necessary for all operators and supervisors to observe the
46、requirements of the Health and Safety at Work etc. Act 1974. The following are guidelines and do not absolve from contractual obligations or responsibilities under the Health and Safety at Work etc. Act 1974. 6.2 Fire hazard. Before any electrical equipment is used, all parties having obligations un
47、der the Health and Safety at Work etc. Act 1974 shall satisfy themselves that there will be no danger as a result of any overheating or sparking. NOTE. Attention is drawn to the British Standard codes of practice, e.g. BS 5345 concerning the use of electrical apparatus and associated equipment for u
48、se in explosive atmospheres of gas or vapour and in mining applications. Attention is also drawn to the dangers of vapour ignition as a result of prods overheating and/or arcing when using the current flow technique and the possibility of igniting accumulations of flammable materials in the vicinity
49、 of the test. This technique should not be used in confined spaces unless adequate ventilation is provided. It is recommended that all electrical equipment has attached to it, or is accompanied by, a fire extinguisher suitable for petrol, gas and electrical fires. Attention is drawn to BS 5423. 6.3 Electrical safety. All equipment involving the use of mains electricity shall comply with the relevant regulations in the latest version of the Health and Safety at Work etc. Act 1974. Where equipment has a mains supply of 1 1 O V and above, it shall be fitted with an earth-leakage
